Derivative Instruments and Hedging Activities - Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023
Derivative assets:
Total derivative assets — gross	$ 173	$ 298	$ 422
Gross amounts offset in the balance sheet	(111)	(124)	(190)
Cash collateral received	(6)	(40)	(55)
Total derivative assets — net	56	134	177
Derivative liabilities:
Total derivative liabilities — gross	(226)	(276)	(457)
Gross amounts offset in the balance sheet	111	124	190
Cash collateral pledged	56	53	102
Total derivative liabilities — net	(59)	(99)	(165)
Commodity contracts
Derivative assets:
Total derivative assets — gross	8	6	19
Derivative liabilities:
Total derivative liabilities — gross	(14)	(8)	(36)
Derivatives designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	22	42	34
Derivatives designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	11	14	9
Derivatives designated as hedging instruments: | Interest rate contracts
Derivative assets:
Total derivative assets — gross	11	28	25
Derivative liabilities:
Total derivative liabilities — gross	(3)	0	(21)
Derivatives not designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	143	250	369
Derivative liabilities:
Total derivative liabilities — gross	(209)	(268)	(400)
Derivatives not designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	5	24	14
Derivative liabilities:
Total derivative liabilities — gross	(1)	(2)	(4)
Derivatives not designated as hedging instruments: | Commodity contracts
Derivative assets:
Total derivative assets — gross	138	226	355
Derivative liabilities:
Total derivative liabilities — gross	$ (208)	(266)	$ (396)
Derivatives not designated as hedging instruments: | Commodity contracts | Prepaid expenses and other current assets
Derivative assets:
Total derivative assets — gross		10
Derivatives not designated as hedging instruments: | Commodity contracts | Other current liabilities
Derivative liabilities:
Total derivative liabilities — gross		$ (12)